Backlight device and backlight control method

ABSTRACT

A backlight device includes a plurality of light sources that emit light of different colors from each other, a plurality of color sensors that receive mixed-color light including light emitted from the light sources to detect light emission states of the light sources, a temperature sensor that measures a temperature in a proximity of the plurality of light sources, a brightness conversion unit that separates the mixed-color light to obtain a detection value for each of the light sources by converting values indicating the detected light emission states, and a calculation unit that corrects the obtained detection value by using information indicating a relationship between the measured temperature and a correction value, the calculation unit determining drive values for the light sources based on the corrected detection value.

The present application is a Continuation Application of U.S. patentapplication Ser. No. 14/352,301, filed on Apr. 16, 2014, which is basedon International Application No. PCT/JP2011/074312, filed on Oct. 21,2011, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a backlight device and a backlightcontrol method.

BACKGROUND ART

Liquid crystal display devices of conventional art include an RGB colorfilter substrate, a liquid crystal layer, and a backlight device. It isproposed in the backlight device of this type of liquid crystal displaydevice that red (R), green (G), and blue (B) colors are mixed to emitwhite color light to improve the display color reproduction range in theliquid crystal display device.

In the backlight devices of the conventional art, brightness of emittedlight is detected by color sensors with color filters that comply withspectral characteristics corresponding to each color of RGB LEDs (lightemitting diodes). Then, a calculation means of the backlight devicecontrols output to the backlight of each color so that the brightnessand chromaticity of the mixed white color light take predeterminedvalues. After light emission is started, the temperature of a connectionunit in the light emitting diode interior rises due to the heatgenerated by the light emitting diode itself, causing the brightness ofeach light emitting diode to change. Consequently, there is a device inwhich the current light emission amount is controlled to be a predefinedstandard light emission amount (for example, refer to Patent Document1).

Prior Art Document [Patent Document]

[Patent Document 1] Japanese Unexamined Patent Application, FirstPublication No. 2008-262032

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

However, in the technique disclosed in Patent Document 1, the colortemperature takes time to converge, for some color temperatures that areset to white by the operation unit of the liquid crystal display device.

The present invention takes into consideration the above problem, and anexemplary object thereof is to provide a backlight device and abacklight control method capable of reducing the length of time taken toconverge to a set color temperature, regardless of the set colortemperature of white.

Means for Solving the Problem

In order to achieve the above object, a backlight device according tothe present invention includes: alight emitting unit of a plurality oflight sources of different light emission colors; a detection unit thatdetects light emission states of the plurality of light sources; atemperature sensor that measures a temperature in a proximity of theplurality of light sources; a brightness conversion unit that convertsvalues indicating the light emission states detected by the detectionunit into a detection value for each component of the light emissioncolors; and a calculation unit that performs temperature correction onthe detection value converted by the brightness conversion unit for eachof the light emission colors by using information when determining drivevalues for the light sources based on the detection values, theinformation indicating a relationship between the temperature measuredby the temperature sensor and a correction value.

In order to achieve the above object, the present invention provides abacklight control method for a backlight device that controls a lightemission amount of a light emitting unit of a plurality of light sourcesof different light emission colors, which includes: a detection step ofdetecting, by a detection unit, light emission states of the pluralityof light sources; a temperature measuring step of measuring, by atemperature sensor, a temperature in a proximity of the plurality oflight sources; a brightness conversion step of converting, by abrightness conversion unit, values indicating the light emission statesdetected in the detection step into a detection value for each componentof the light emission colors; and a calculation step of performingtemperature correction, by a calculation unit, on the detection valueconverted in the brightness conversion step for each of the lightemission colors by using information when determining drive values forthe light sources based on the detection values, the informationindicating a relationship between the temperature measured in thetemperature measuring step and a correction value.

Effect of the Invention

The backlight device of the present invention is such that theconversion unit converts the light emission state detected by thedetection unit into a detection value for each light source. Thecalculation unit performs temperature correction on the detection valuesconverted by the conversion unit using a predefined temperaturecorrection coefficient for each light emission color, when determiningdrive values for the light sources based on the detection values. As aresult, the length of time taken to converge to a set color temperaturecan be reduced regardless of the set color temperature of white.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a schematic configuration of a backlightdevice according to a first exemplary embodiment.

FIG. 2 is a diagram showing an example of a light transmissioncharacteristic of an RGB color filter.

FIG. 3 is a diagram for describing temperature drift in a red colorsensor according to the first exemplary embodiment.

FIG. 4 is a diagram for describing temperature correction made to a redlight emission color in the red color sensor according to the firstexemplary embodiment.

FIG. 5 is a diagram for describing an example of color temperaturechanges in a case where a temperature correction is made regarding atemperature drift characteristic of a color sensor.

FIG. 6 is a diagram for describing an example of color temperaturechanges in a case where a temperature correction is made for each colorof the backlight according to the first exemplary embodiment.

FIG. 7 is a block diagram of a schematic configuration of a backlightdevice according to a second exemplary embodiment.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

First, a brief overview of the present invention is described.

In a backlight device used in such as a liquid crystal display device,the light amount of backlight is detected with a color sensor thatincludes a color filter. Due to the spectral characteristic of the colorfilter, the color sensor also detects the light amount of backlightother than that of the color that needs to be detected. In the presentexemplary embodiment, the conversion unit converts a detection valuedetected by the color sensor into a light amount for each color emittedby the backlight, using a conversion equation. Then the temperaturecorrection unit performs temperature correction on the detection valuefor each color that is converted by the conversion unit.

Thereby, the brightness of the backlight with respect to temperaturechange is precisely controlled to suppress influence of temperaturedrift with respect to a white point setting.

First Exemplary Embodiment

Hereunder, exemplary embodiments of the present invention are describedin detail, with reference to the drawings.

FIG. 1 is a block diagram of a schematic configuration of a backlightdevice 1 according to the present exemplary embodiment. As shown in FIG.2, the backlight device 1 includes a backlight driving unit 10, a lightemitting unit 20, a detection unit 30, a backlight target color settingunit 40, a temperature sensor 55, and a calculation unit 50.

The backlight driving unit 10 includes a red backlight driving circuit101, a green backlight driving circuit 102, and a blue backlight drivingcircuit 103. The red backlight driving circuit 101 drives a redbacklight 201 of the light emitting unit 20, based on driving signalsoutput from a red backlight drive value calculation unit 541 of thecalculation unit 50. The green backlight driving circuit 102 drives agreen backlight 202, based on driving signals output from a greenbacklight drive value calculation unit 542. The blue backlight drivingcircuit 103 drives a blue backlight 203, based on driving signals outputfrom a blue backlight drive value calculation unit 543.

The light emitting unit 20 includes a red backlight 201, a greenbacklight 202, and a blue backlight 203.

The red backlight 201 is a light source that emits red color light basedon driving signals output from the red backlight driving circuit 101.The center wavelength of red color light is, for example, approximately660 [nm]. The green backlight 202 is a light source that emits greencolor light based on driving signals output from the green backlightdriving circuit 102. The center wavelength of green color light is, forexample, approximately 540 [nm]. The blue backlight 203 is a lightsource that emits blue color light based on driving signals output fromthe blue backlight driving circuit 103. The center wavelength of bluecolor light is, for example, approximately 460 [nm].

The red backlight 201, the green backlight 202, and the blue backlight203 are, for example, light emitting diodes (LEDs) or semiconductorlasers.

The detection unit 30 includes a red color sensor 301, a green colorsensor 302, and a blue color sensor 303.

The red color sensor 301 has a color filter of a spectral sensitivitycharacteristic corresponding to the light emission color of the redbacklight 201. The spectral sensitivity characteristic of the colorfilter of the red color sensor 301 is such that, for example, as withthe curved line g103 in FIG. 1, the band with transmittance 20[%] orhigher is approximately 590 [nm] to 720 [nm]. The red color sensor 301receives light emitted from the light emitting unit 20, and detects thelight emission state of the light emitting unit. The red color sensor301 then converts the received light amount into an electric signal, andoutputs the converted electric signal to the calculation unit 50 as adetection value Rs. The light emission state detected by the detectionunit 30 is a detection value such as brightness or chromaticity. Adetection value is described as brightness in the following description.

The green color sensor 302 has a color filter of a spectral sensitivitycharacteristic corresponding to the light emission color of the greenbacklight 202. The spectral sensitivity characteristic of the colorfilter of the green color sensor 302 is such that, for example, as withthe curved line g102 in FIG. 1, the band with transmittance 20[%] orhigher is approximately 480 [nm] to 600 [nm] like the curved line g102.The green color sensor 302 receives light emitted from the lightemitting unit 20, then converts the received light amount into anelectric signal, and outputs the converted electric signal to thecalculation unit 50 as a detection value Gs.

The blue color sensor 303 has a color filter of a spectral sensitivitycharacteristic corresponding to the light emission color of the bluebacklight 203. The spectral sensitivity characteristic of the colorfilter of the blue color sensor 303 is such that, for example, as withthe curved line g101 in FIG. 1, the band with transmittance 20[%] orhigher is approximately 400 [nm] to 540 [nm]. The blue color sensor 303receives light emitted from the light emitting unit 20, then convertsthe received light amount into an electric signal, and outputs theconverted electric signal to the calculation unit 50 as a detectionvalue Bs.

Moreover, the red color sensor 301, the green color sensor 302, and theblue color sensor 303 are, for example, photo sensors.

The backlight target color setting unit 40 stores setting values for thered backlight 201, the green backlight 202, and the blue backlight 203when emitting white color light, which have been preliminarily set by auser of the backlight device 1 for example. The backlight target colorsetting unit 40 outputs the set setting values to a red sensor targetvalue calculation unit 531, a green sensor target value calculation unit532, and a blue sensor target value calculation unit 533 of thecalculation unit 50.

The setting values are, for example, values that are adjusted by a userwhile looking at a display of a display unit (not shown in the figure)so that the user feels the brightness of the red backlight 201, thegreen backlight 202, and the blue backlight 203 as white color lightemission, and these values are set on an operation unit (not shown inthe figure).

The temperature sensor 55 is attached in the proximity of the lightemitting unit 20. The temperature sensor 55 detects temperatures, andoutputs information indicating detected temperatures to a temperaturecorrection unit 510.

The calculation unit 50 includes a sensor value/BL brightness conversionunit 500 (conversion unit), a temperature correction unit 510, a BLbrightness/sensor value conversion unit 520, a sensor target valuecalculation unit 530, and a drive value calculation unit 540.

The sensor value/BL brightness conversion unit 500 includes a red colordetection value temperature correction unit 511, a green color detectionvalue temperature correction unit 512, and a blue color detection valuetemperature correction unit 513. The sensor value/BL brightnessconversion unit 500 stores conversion equations, which have beenpreliminarily calculated by means of actual measurement and simulation.

$\begin{matrix}\lbrack {{Equation}\mspace{14mu} 1} \rbrack & \; \\{\begin{bmatrix}R \\G \\B\end{bmatrix} = {\begin{bmatrix}1.007 & 0.016 & 0.005 \\{- 0.155} & 1.225 & {- 0.017} \\{- 0.046} & 0.014 & 1.093\end{bmatrix} \times \begin{bmatrix}{Rs} \\{Gs} \\{Bs}\end{bmatrix}}} & (1)\end{matrix}$

In Equation (1), Rs denotes a detection value of the red color sensor301, Gs denotes a detection value of the green color sensor 302, and Bsdenotes a detection value of the blue color sensor 303. Furthermore, inEquation (1), R denotes a detection value of the component of the redcolor sensor 301, G denotes a detection value of the component of thegreen color sensor 302, and B denotes a detection value of the componentof the blue color sensor 303. Hereunder, the red color sensor 301, thegreen color sensor 302, and the blue color sensor 303 are collectivelyreferred to as color sensors 300.

A sensor value/BL brightness first conversion unit 501 converts thedetection value Rs detected by the red color sensor 301, the detectionvalue Gs detected by the green color sensor 302, and the detection valueBs detected by the blue color sensor 303 into a detection value R of thered backlight component, using Equation (1). The sensor value/BLbrightness first conversion unit 501 outputs the converted detectionvalue R of the component of the red backlight 201, to the red colordetection value temperature correction unit 511.

Similarly, a sensor value/BL brightness second conversion unit 502converts the detection value of the detection unit 30 into a detectionvalue G of the green backlight component, using Equation (1). The sensorvalue/BL brightness second conversion unit 502 outputs the converteddetection value G to the green color detection value temperaturecorrection unit 512. A sensor value/BL brightness third conversion unit503 converts the detection value of the detection unit 30 into adetection value B of the blue backlight component, using Equation (1).The sensor value/BL brightness third conversion unit 503 outputs theconverted detection value B to the blue color detection valuetemperature correction unit 513.

The temperature correction unit 510 includes the red color detectionvalue temperature correction unit 511, the green color detection valuetemperature correction unit 512, and the blue color detection valuetemperature correction unit 513. The temperature correction unit 510receives input of information that indicates temperatures detected bythe temperature sensor 55.

The red color detection value temperature correction unit 511 stores atemperature correction coefficient (correction value) for the detectionvalue of the component of the red backlight 201 and a temperature thatare associated with each other. This temperature correction coefficientis calculated preliminarily by means of actual measurement orsimulation. The red color detection value temperature correction unit511 corrects the detection value R output from the sensor value/BLbrightness first conversion unit 501, using the information thatindicates the temperature detected by the temperature sensor 55 and atemperature correction equation or a temperature correction coefficientfor the component of the red backlight 201. The red color detectionvalue temperature correction unit 511 outputs the corrected detectionvalue R′ to the BL brightness/sensor value conversion unit 520.

The green color detection value temperature correction unit 512 stores atemperature correction coefficient for the detection value of thecomponent of the green backlight 202 and a temperature that areassociated with each other. The green color detection value temperaturecorrection unit 512 corrects the detection value G output from thesensor value/BL brightness second conversion unit 502, using theinformation that indicates the temperature detected by the temperaturesensor 55 and a temperature correction equation or a temperaturecorrection coefficient for the component of the green backlight 202. Thegreen color detection value temperature correction unit 512 outputs thecorrected detection value G′ to the BL brightness/sensor valueconversion unit 520.

The blue color detection value temperature correction unit 513 stores atemperature correction coefficient for the detection value of thecomponent of the blue backlight 203 and a temperature that areassociated with each other. The blue color detection value temperaturecorrection unit 513 corrects the detection value B output from thesensor value/BL brightness third conversion unit 503, using theinformation that indicates the temperature detected by the temperaturesensor 55 and a temperature correction equation or a temperaturecorrection coefficient for the component of the blue backlight 203. Theblue color detection value temperature correction unit 513 outputs thecorrected detection value B′ to the BL brightness/sensor valueconversion unit 520.

The BL brightness/sensor value conversion unit 520 includes a BLbrightness/sensor value first conversion unit 521, a BLbrightness/sensor value second conversion unit 522, and a BLbrightness/sensor value third conversion unit 523. The BLbrightness/sensor value conversion unit 520 stores conversion equations,which have been preliminarily calculated by means of actual measurementor simulation.

$\begin{matrix}\lbrack {{Equation}\mspace{14mu} 2} \rbrack & \; \\{\begin{bmatrix}{Rs}^{\prime} \\{Gs}^{\prime} \\{Bs}^{\prime}\end{bmatrix} = {\begin{bmatrix}1.007 & 0.016 & 0.005 \\{- 0.155} & 1.225 & {- 0.017} \\{- 0.046} & 0.014 & 1.093\end{bmatrix}^{- 1} \times \begin{bmatrix}R^{\prime} \\G^{\prime} \\B^{\prime}\end{bmatrix}}} & (2)\end{matrix}$

The BL brightness/sensor value first conversion unit 521 converts thetemperature-corrected detection values (R′, G′, and B′), which areoutput from the temperature correction unit 510, into a detection valueRs′ of the red color sensor, using Equation (2). The BLbrightness/sensor value first conversion unit 521 outputs the converteddetection value Rs′ to the red backlight drive value calculation unit541.

Similarly, the BL brightness/sensor value second conversion unit 522converts the temperature-corrected detection values (R′, G′, and B′),which are output from the temperature correction unit 510, into adetection value Gs′ of the green color sensor, using Equation (2). TheBL brightness/sensor value second conversion unit 522 outputs theconverted detection value Gs′ to the green backlight drive valuecalculation unit 542. The

BL brightness/sensor value third conversion unit 523 converts thetemperature-corrected detection values (R′, G′, and B′), which areoutput from the temperature correction unit 510, into a detection valueBs′ of the blue color sensor, using Equation (2). The BLbrightness/sensor value third conversion unit 523 outputs the converteddetection value Bs′ to the blue backlight drive value calculation unit543.

The sensor target value calculation unit 530 (target value calculationunit) includes a red sensor target value calculation unit 531, a greensensor target value calculation unit 532, and a blue sensor target valuecalculation unit 533. The red sensor target value calculation unit 531calculates a target value for the detection value of the red colorsensor 301, based on a setting value for the red backlight 201 at thetime of white color light emission, which is output from the backlighttarget color setting unit 40. The red sensor target value calculationunit 531 outputs the calculated target value for the detection value ofthe red color sensor 301 to the red backlight drive value calculationunit 541. The green sensor target value calculation unit 532 calculatesa target value for the detection value of the green color sensor 302,based on a setting value for the green backlight 202 at the time ofwhite color light emission, which is output from the backlight targetcolor setting unit 40. The green sensor target value calculation unit532 outputs the calculated target value for the detection value of thegreen color sensor 302 to the green backlight drive value calculationunit 542. The blue sensor target value calculation unit 533 calculates atarget value for the detection value of the blue color sensor 303, basedon a setting value for the blue backlight 203 at the time of white colorlight emission, which is output from the backlight target color settingunit 40. The blue sensor target value calculation unit 533 outputs thecalculated target value for the detection value of the blue color sensor303 to the blue backlight drive value calculation unit 543.

The drive value calculation unit 540 includes a red backlight drivevalue calculation unit 541, a green backlight drive value calculationunit 542, and a blue backlight drive value calculation unit 543.

The red backlight drive value calculation unit 541 compares the targetvalue for the detection value of the red color sensor 301, which isoutput from the red sensor target value calculation unit 531, with thedetection value Rs′, which is output from the BL brightness/sensor valuefirst conversion unit 521. The red backlight drive value calculationunit 541 generates a driving signal of the red backlight 201 based onthe result of the comparison. The red backlight drive value calculationunit 541, for example, generates a driving signal of the red backlight201 that makes the difference between the detection value of the redcolor sensor 301 and the detection value Rs′ zero. Specifically, if thedetection value Rs′ is higher than the detection value of the red colorsensor 301, the red backlight drive value calculation unit 541calculates a driving signal that is smaller than the value of the signalcurrently driving the red backlight 201, in order to lower thebrightness value. If the detection value Rs′ is lower than the detectionvalue of the red color sensor 301, the red backlight drive valuecalculation unit 541 calculates a driving signal that is greater thanthe value of the signal currently driving the red backlight 201, inorder to raise the brightness value. The red backlight drive valuecalculation unit 541 outputs the generated driving signal to the redbacklight driving circuit 101 of the backlight driving unit 10.

The green backlight drive value calculation unit 542 compares the targetvalue for the detection value of the green color sensor 302, which isoutput from the green sensor target value calculation unit 532, with thedetection value Gs′, which is output from the BL brightness/sensor valuesecond conversion unit 522. The green backlight drive value calculationunit 542 generates a driving signal of the green backlight 202 based onthe result of the comparison, and outputs the generated driving signalto the green backlight driving circuit 102.

The blue backlight drive value calculation unit 543 compares the targetvalue for the detection value of the blue color sensor 303, which isoutput from the blue sensor target value calculation unit 533, with thedetection value Bs′, which is output from the BL brightness/sensor valuethird conversion unit 523. The blue backlight drive value calculationunit 543 generates a driving signal of the blue backlight 203 based onthe result of the comparison, and outputs the generated driving signalto the blue backlight driving circuit 103.

Next, the spectral characteristic of the color filter provided in thecolor sensor 300 is described, with reference to FIG. 2. FIG. 2 is adiagram showing an example of a light transmission characteristic of anROB color filter.

In FIG. 2, the horizontal axis represents wavelength, the vertical axisrepresents light transmittance, the curved line g101 represents lighttransmittance with respect to the wavelength of the blue filter, thecurved line g102 represents light transmittance with respect to thewavelength of the green filter, and the curved line g103 representslight transmittance with respect to the wavelength of the red filter. Asshown in FIG. 2, the band where the blue filter transmittance is 20[%]or higher is approximately 400 [nm] to 540 [nm] as seen from the curvedline g101. The band where the green filter transmittance is 20[%] orhigher is approximately 480 [nm] to 600 [nm] as seen from the curvedline g102. The band where the red filter transmittance is 20[%] orhigher is approximately 590 [nm] to 720 [nm] as seen from the curvedline g103. The respective filters have the spectral characteristic shownin FIG. 2, and therefore, the green color sensor also detects the lightamount with approximate wavelength 450 [nm] to 540 [nm] for example.Moreover, the red color sensor also detects few [%] of the light amountwith approximate wavelength 380 [nm] to 540 [nm] of the blue band.Furthermore, the red color sensor also detects few [%] to 20[%] of thelight amount with approximate wavelength 570 [nm] to 600 [nm] of thegreen band.

Therefore, in the present exemplary embodiment, the sensor value/BLbrightness conversion unit 500 separates the detection value detected bythe detection unit 30 into the respective color components of thebacklight, using Equation (1).

Next, temperature drift of a detection value in the color sensor 300 isdescribed, with reference to FIG. 3. FIG. 3 is a diagram for describingtemperature drift in a red color sensor according to the presentexemplary embodiment.

In FIG. 3, the horizontal axis represents temperature within thebacklight device 1, and the vertical axis represents the magnitude of adetection value of the red color sensor. Moreover, in FIG. 3, the dashedline g201 represents a reference value, which is a detection value atthe time of supplying a constant drive value to the backlight at apredetermined environmental temperature. The curved line g211 representsa temperature drift characteristic of the detection value detected bythe red color sensor 301 at the time of driving only the red backlight201. The curved line g212 represents a temperature drift characteristicof the detection value detected by the red color sensor 301 at the timeof driving only the green backlight 202. The curved line g213 representsa temperature drift characteristic of the detection value detected bythe red color sensor 301 at the time of driving only the blue backlight203.

As shown in FIG. 3, the temperature drift characteristic of thedetection value differs with each color of light received by the redcolor sensor 301. Similarly, the temperature drift characteristic of thedetection value differs with each color of light received by the greencolor sensor 302, and the temperature drift characteristic of thedetection value differs with each color of light received by the bluecolor sensor 303.

Next, an example of the calculation method of Equation (1) is described.When the detection values Rs₁, Gs₁, and Bs₁ of the respective colorsensors are measured while only the red backlight 201 is made to emitlight, the brightness component R₁ of the red backlight 201 is expressedas Equation (3) below. The brightness value of the red backlight 201 isa value found by multiplying the drive value by a predefined constant(for example, amplification multiplier of the driving circuit).Accordingly, the brightness component R₁ of the red backlight 201 iscalculated by multiplying the drive value by the constant. The drivevalue is, for example, a known value such as driving current value ordriving voltage value.

R ₁ =a ₁₁ ×Rs ₁ +a ₁₂ ×Gs ₁ +a ₁₃ ×Bs ₁   (3)

In Equation (3), a₁₁, a₁₂, and a₁₃ are constants.

Next, when the detection values Rs₂, Gs₂, and Bs₂ of the respectivecolor sensors are measured while only the green backlight 202 is made toemit light, the brightness component G₁ of the green backlight 202 isexpressed as Equation (4) below. Similarly, the brightness component G₁of the green backlight 202 is calculated by multiplying the drive valueby the constant.

G ₁ =a ₂₁ ×Rs ₂ +a ₂₂ ×Gs ₂ +a ₂₃ ×Bs ₂   (4)

In Equation (4), a₂₁, a₂₂, and a₂₃ are constants.

Next, when the detection values Rs₃, Gs₃, and Bs₃ of the respectivecolor sensors are measured while only the blue backlight 203 is made toemit light, the brightness component B₁ of the blue backlight 203 isexpressed as Equation (5) below. Similarly, the brightness component B₃of the blue backlight 203 is calculated by multiplying the drive valueby the constant.

B ₃ =a ₃₁ ×Rs ₃ +a ₃₂ ×Gs ₃ +a ₃₃ ×Bs ₃   (5)

In Equation (5), a₃₁, a₃₂, and a₃₃ are constants.

Each constant in the simultaneous equations of Equation (3) throughEquation (5) is calculated, using the detection value of each colorsensor obtained while only each backlight is made to emit light at eachof the three types of brightness, and using the brightness component ofthe red backlight 201, the green backlight 202, or the blue backlight203. The result of performing calculation in this manner is a₁₁=1.007,a₁₂=0.016, a₁₃=0.005, a₂₁=−0.155, a₂₂=1.225, a₂₃=−0.017, a₃₁=−0.046,a₃₂=0.014, and a₃₃=1.093 as shown in Equation (1). The value of eachelement of Equation (1) is an example, and it may differ, depending onthe characteristic, the light receiving sensitivity, and the lightreceiving band of each color filter of the red color sensor 301, thegreen color sensor 302, and the blue color sensor 303.

Next, temperature correction performed by the temperature correctionunit 510 is described, with reference to FIG. 4.

FIG. 4 is a diagram for describing temperature correction made to a redlight emission color in the red color sensor according to the presentexemplary embodiment. In FIG. 4, the horizontal axis representstemperature within the backlight device 1, and the vertical axisrepresents the magnitude of a detection value and the magnitude of acorrection value in a case where the red light emission color is red inthe red color sensor. Moreover, in FIG. 4, the dashed line g201represents a reference value as with FIG. 3, and the curved line g211represents the temperature drift characteristic of the detection valueof the red color light emission color of the red color sensor 301 aswith FIG. 3. The curved line 221 represents the relationship betweentemperature and temperature correction coefficient stored in the redcolor detection value temperature correction unit 511.

As shown in FIG. 4, the temperature correction coefficient stored in thered color detection value temperature correction unit 511 is a value forcorrecting the detection value of the red color light emission color(detection value of the component of the red backlight 201) to areference value a, for each temperature measured by the temperaturesensor 55. For example, when the temperature within the device measuredby the temperature sensor 55 is c1, the detection value of the red colorlight emission color takes a detection value b due to the influence oftemperature drift. The value of the temperature correction coefficientin this case is c. The red color detection value temperature correctionunit 511 can perform temperature correction on the detection value b bymultiplying the detection value b by the correction coefficient c.Moreover, when the temperature within the device is c2, the temperaturecorrection coefficient value is 1 since the detection value a matchesthe reference value a.

The temperature correction coefficient stored in the red color detectionvalue temperature correction unit 511 may be a temperature correctionequation that expresses the relationship between temperature and acorrection coefficient to be multiplied. In this case, the red colordetection value temperature correction unit 511 uses the storedtemperature correction equation to calculate the temperature correctioncoefficient based on the temperature measured by the temperature sensor55. The red color detection value temperature correction unit 511 thenmultiplies the detection value by the calculated temperature correctioncoefficient to thereby perform temperature correction of the detectionvalue.

Alternatively, the red color detection value temperature correction unit511 may add the stored temperature correction coefficient to thedetection value to perform temperature correction. In this case, whenthe temperature within the device is c1, the temperature correctioncoefficient to be added is c′ (not shown in the figure). The red colordetection value temperature correction unit 511 then adds thetemperature correction coefficient c′ to the detection value b tothereby perform temperature correction. Moreover, when the temperaturewithin the device is c2, the temperature correction coefficient value tobe added is 0 since the detection value a matches the reference value a.The red color detection value temperature correction unit 511 may storetemperature and the temperature correction coefficient for correctingtemperature by being added to the detection value in this manner, whileassociating them with each other. Also in this case, the temperaturecorrection coefficient stored in the red color detection valuetemperature correction unit 511 may be a temperature correction equationthat expresses the relationship between the temperature and thecorrection coefficient to be added.

Similarly, in the case of the green detection value temperaturecorrection unit 512,the temperature drift characteristic for thedetection value of the red backlight 201, the temperature driftcharacteristic for the detection value of the green back light 202, andthe temperature drift characteristic for the detection value of the bluebacklight 203, of the green color sensor 302 are also different. Thegreen color detection value temperature correction unit 512 performstemperature correction on the detection value Gs of the component of thegreen backlight 202, using the temperature correction equation ortemperature correction coefficient for the component of the greenbacklight 202.

Similarly, in the case of the blue detection value temperaturecorrection unit 513, the temperature drift characteristic for thedetection value of the red backlight 201, the temperature driftcharacteristic for the detection value of the green back light 202, andthe temperature drift characteristic for the detection value of the bluebacklight 203, of the green color sensor 302 are different. The bluecolor detection value temperature correction unit 513 performstemperature correction on the detection value Gs of the component of theblue backlight 203, using the temperature correction equation ortemperature correction coefficient for the component of the bluebacklight 203.

Next, a temperature correction method for the backlight device 1 of thepresent exemplary embodiment is described. First, steps of temperaturecorrection for the brightness of the red backlight 201 are described.

The detection unit 30 receives light emitted from the light emittingunit 20, and then outputs a detection value that has been converted fromthe received light amount into an electric signal, to the calculationunit 50.

Subsequently, a sensor value/BL brightness first conversion unit 501 ofthe calculation unit 50 converts the detection value output from thedetection unit 30 into a detection value Rs of the component of the redbacklight 201, using Equation (1). The sensor value/BL brightness firstconversion unit 501 then outputs the converted detection value Rs of thecomponent of the red backlight 201 to the red color detection valuetemperature correction unit 511.

Then, the red color detection value temperature correction unit 511performs temperature correction on the detection value Rs of thecomponent of the red backlight 201, using the information that indicatesthe temperature detected by the temperature sensor 55 and apreliminarily stored temperature correction equation or temperaturecorrection coefficient, and outputs the corrected detection value Rs′ tothe BL brightness/sensor value first conversion unit 521.

Next, the BL brightness/sensor value first conversion unit 521 convertsthe temperature-corrected detection value Rs′ output from thetemperature correction unit 510 into a detection value Rs′, which is adetection value of the red color sensor 301, using Equation (2). The BLbrightness/sensor value first conversion unit 521 outputs the converteddetection value Rs′ to the red backlight drive value calculation unit541.

Then, the red backlight drive value calculation unit 541 compares thetarget value for the detection value of the red color sensor 301, whichis output from the red sensor target value calculation unit 531, withthe detection value Rs′, which is output from the BL brightness/sensorvalue first conversion unit 521, and generates a driving signal of thered backlight 201 based on the result of the comparison.

With the above process, the backlight device 1 can perform temperaturecorrection for the temperature drift of the red color sensor 301.

Similarly, the sensor value/BL brightness second conversion unit 502converts the detection value output from the detection unit 30 into adetection value G of the component of the green backlight 202. Thesensor value/BL brightness third conversion unit 503 converts thedetection value output from the detection unit 30 into a detection valueB of the component of the blue backlight 203. Next, the green colordetection value temperature correction unit 512 and the blue colordetection value temperature correction unit 513 performs temperaturecorrection on each detection value of each backlight component, whichhas been converted in the above manner, using the information indicatingthe temperature detected by the temperature sensor 55, and thepreliminarily stored temperature correction equation or temperaturecorrection coefficient. In this manner, the backlight device 1 uses thecorrected detection values Gs′ and Bs′ to perform temperature correctionfor the brightness of the green and blue backlights as with thebrightness of the red back light 201.

Next, an example of color temperature changes in the backlight device 1due to temperature drift is described, with reference to FIG. 5 and FIG.6.

FIG. 5 is a diagram for describing an example of color temperaturechanges in a case where a temperature correction is made to atemperature drift characteristic of a color sensor. FIG. 6 is a diagramfor describing an example of color temperature changes in a case where atemperature correction is made to each color of the backlight accordingto the present exemplary embodiment.

In FIG. 5 and FIG. 6, the horizontal axis represents warm-up time, andthe vertical axis represents color temperature level. The warm-up timerefers to a length of time elapsed after the power supply of thebacklight device 1 is switched on.

In FIG. 5, the dashed line g301 represents a setting value where thecolor temperature is set to 3,000 [K (Kelvin)], and the dashed line g302represents a setting value where the color temperature is set to 6,500[K]. Moreover, the curved line g311 represents changes in the colortemperature characteristic in the display unit (not shown in the figure)where the color temperature is set to 3,000 [K]. The curved line g312represents changes in the color temperature characteristic in thedisplay unit where the color temperature is set to 6,500 [K].

In FIG. 6, the dashed line g401 represents a setting value where thecolor temperature is set to 3,000 [K (Kelvin)], and the dashed line g402represents a setting value where the color temperature is set to 6,500[K]. Moreover, the curved line g411 represents changes in the colortemperature characteristic in the display unit where the colortemperature is set to 3,000 [K]. The curved line g412 represents changesin the color temperature characteristic in the display unit where thecolor temperature is set to 6,500 [K].

FIG. 5 shows changes in the color temperature in the display unit withrespect to the warm-up time in the supposed case where the temperaturecorrection unit provided in the backlight device performs temperaturecorrection for the temperature drift characteristic of the detectionvalue of each color sensor. In this case, for example, temperaturecorrection is performed on the detection value of the red color sensorbased on the temperature drift characteristic of the detection value atthe time of the red color sensor receiving white color light. Similarly,temperature correction is performed on the detection value of the greencolor sensor based on the temperature drift characteristic of thedetection value at the time of the green color sensor receiving whitecolor light. Furthermore, temperature correction is performed on thedetection value of the blue color sensor based on the temperature driftcharacteristic of the detection value at the time of the blue colorsensor receiving white color light.

When a user sets white point chromaticity in an image display devicehaving a backlight device that performs temperature correction in thismanner, if the color temperature is set to 6,500 [K], the colortemperature of the display unit converges to the setting value at timet1 as illustrated with the curved line g312. However, if the colortemperature is set to 3,000 [K], the color temperature of the displayunit still does not take the setting value even at time t2 asillustrated with the curved line g311. In this way, the colortemperature convergence time for the warm-up time differs for each setwhite point setting.

On the other hand, as shown in FIG. 6, in the case where the detectionvalue of each color sensor is converted into a detection value of thecomponent of the backlight and it is temperature-corrected to theconverted detection value of the backlight component as practiced in thepresent exemplary embodiment, if the color temperature is set to 6,500[K], the color temperature of the display unit takes the setting valueat time ti as illustrated with the curved line g413. Next, if the colortemperature is set to 3,000 [K], the color temperature of the displayunit takes the setting value at time t3, at which a shorter length oftime has elapsed than time t2, as illustrated with the curved line g403.In this manner, according to the present exemplary embodiment, it ispossible to reduce the length of time taken by the color temperature ofthe display unit to converge, and match the convergence time for eachwhite point setting.

As described above, the backlight device 1 of the present exemplaryembodiment converts the detection value detected by the color sensorinto a detection value of the component of each backlight. The backlightdevice 1 of the present exemplary embodiment perform temperaturecorrection on the converted detection value of the backlight component,using a temperature correction equation or temperature correctioncoefficient that is preliminarily set for each color component. Thedrive value calculation unit 540 compares each target value output fromthe sensor target value calculation unit 530 with each correcteddetection value output from the BL brightness/sensor value conversionunit 520. The drive value calculation unit 540 generates each drivingsignal for the light emitting unit 20 based on the comparison result,and drives each backlight of the light emitting unit 20 with eachgenerated driving signal.

As a result, the backlight device 1 of the present exemplary embodimentcan suppress temperature drift of the brightness of each backlight withrespect to the temperature, and therefore, can reduce the convergencetime to achieve the set white point.

Second Exemplary Embodiment

FIG. 7 is a block diagram of a schematic configuration of a backlightdevice la according to the present exemplary embodiment. As shown inFIG. 7, the backlight device la includes a backlight driving unit 10, alight emitting unit 20, a detection unit 30, a backlight target colorsetting unit 40, and a calculation unit 50 a. Moreover, the calculationunit 50 a includes a sensor value/BL brightness conversion unit 500(conversion unit), a temperature correction unit 510 a, a drive valuecalculation unit 540 a, and a backlight target value calculation unit550.

The same reference symbols are given to the functional units with thesame function in the backlight device 1 described in the first exemplaryembodiment, and descriptions thereof are omitted.

The temperature correction unit 510 a includes a red color detectionvalue temperature correction unit 511 a, a green color detection valuetemperature correction unit 512 a, and a blue color detection valuetemperature correction unit 513 a.

As with the first exemplary embodiment, the red color detection valuetemperature correction unit 511 a corrects the detection value Rs outputfrom the sensor value/BL brightness first conversion unit 501, using atemperature correction equation or temperature correction coefficientfor the red backlight component, and outputs the corrected detectionvalue R′ to a red backlight drive value calculation unit 541 a. As withthe first exemplary embodiment, the green color detection valuetemperature correction unit 512 a corrects the detection value Gs outputfrom the sensor value/BL brightness second conversion unit 502, using atemperature correction equation or temperature correction coefficientfor the green backlight component, and outputs the corrected detectionvalue G′ to a green backlight drive value calculation unit 542 a. Aswith the first exemplary embodiment, the blue color detection valuetemperature correction unit 513 a corrects the detection value B outputfrom the sensor value/BL brightness third conversion unit 503, using atemperature correction equation or temperature correction coefficientfor the blue backlight component, and outputs the corrected detectionvalue B′ to a blue backlight drive value calculation unit 543 a.

That is to say, in the present exemplary embodiment, the calculationunit 50 a outputs the detection values (R′, G′, and B′) corrected by thetemperature correction unit 510 a to the drive value calculation unit540 a without converting them to the detection values of the sensorsusing Equation (2) as described in the first exemplary embodiment.

The backlight target value calculation unit 550 (target valuecalculation unit) includes a red backlight target value calculation unit551, a green backlight target value calculation unit 552, and a bluebacklight target value calculation unit 553.

The red backlight target value calculation unit 551 calculates a targetvalue for the brightness of the red backlight 201, based on a settingvalue for the red backlight 201 at the time of white color lightemission, which is output from the backlight target color setting unit40. The red sensor target value calculation unit 531 outputs thecalculated target value for the brightness of the red backlight 201 tothe red backlight drive value calculation unit 541 a. The greenbacklight target value calculation unit 552 calculates a target valuefor the brightness of the green backlight 202, based on a setting valuefor the green backlight 202 at the time of white color light emission,which is output from the backlight target color setting unit 40. Thegreen sensor target value calculation unit 532 outputs the calculatedtarget value for the brightness of the green backlight 202 to the greenbacklight drive value calculation unit 542 a. The blue backlight targetvalue calculation unit 553 calculates a target value for the brightnessof the blue backlight 203, based on a setting value for the bluebacklight 203 at the time of white color light emission, which is outputfrom the backlight target color setting unit 40. The blue sensor targetvalue calculation unit 533 outputs the calculated target value for thebrightness of the blue backlight 203 to the blue backlight drive valuecalculation unit 543 a.

The drive value calculation unit 540 a includes a red backlight drivevalue calculation unit 541 a, a green backlight drive value calculationunit 542 a, and a blue backlight drive value calculation unit 543 a.

The red backlight drive value calculation unit 541 a compares the targetvalue for the brightness of the red backlight 201, which is output fromthe red backlight target value calculation unit 551, with the detectionvalue R′, which is output from the red color detection value temperaturecorrection unit 511 a. The red backlight drive value calculation unit541 a generates a driving signal of the red backlight 201 based on theresult of the comparison, and outputs the generated driving signal tothe red backlight driving circuit 101. The green backlight drive valuecalculation unit 542 a compares the target value for the brightness ofthe green backlight 202, which is output from the green backlight targetvalue calculation unit 552, with the detection value G′, which is outputfrom the green color detection value temperature correction unit 512 a.The green backlight drive value calculation unit 542 a generates adriving signal of the green backlight 202 based on the result of thecomparison, and outputs the generated driving signal to the greenbacklight driving circuit 102. The blue backlight drive valuecalculation unit 543 a compares the target value for the brightness ofthe blue backlight 203, which is output from the blue backlight targetvalue calculation unit 553, with the detection value B′, which is outputfrom the blue color detection value temperature correction unit 513 a.The blue backlight drive value calculation unit 543 a generates adriving signal of the blue backlight 203 based on the result of thecomparison, and outputs the generated driving signal to the bluebacklight driving circuit 103.

That is to say, the drive value calculation unit 540 a of the presentexemplary embodiment compares the detection values (R′, G′, and B′) ofeach temperature-corrected color component of the backlight, with thetarget value output from the backlight target value calculation unit550, to control the driving signal of each backlight.

Next, a temperature correction method for the backlight device 1 a ofthe present exemplary embodiment is described. First, steps oftemperature correction for the brightness of the red backlight 201 aredescribed.

The detection unit 30 receives light emitted from the light emittingunit 20, and outputs a detection value that has been converted from thereceived light amount into an electric signal, to the calculation unit50.

Subsequently, a sensor value/BL brightness first conversion unit 501 ofthe calculation unit 50 converts the detection value output from thedetection unit 30 into a detection value R of the component of the redbacklight 201, using Equation (1). The sensor value/BL brightness firstconversion unit 501 outputs the converted brightness value R of the redbacklight 201, to the red color detection value temperature correctionunit 511 a.

Then, the red color detection value temperature correction unit 511 aperforms temperature correction on the detection value R of thecomponent of the red backlight 201, using the information that indicatesthe temperature detected by the temperature sensor 55 and apreliminarily stored temperature correction equation or temperaturecorrection coefficient, and outputs the corrected detection value R′ tothe red backlight drive value calculation unit 541 a.

Then, the red backlight drive value calculation unit 541 a compares thetarget value for the detection value of the red color sensor 301, whichis output from the red backlight target value calculation unit 551, withthe temperature-corrected detection value R′, which is output from thered color detection value temperature correction unit 511 a, andgenerates a driving signal of the red backlight 201 based on the resultof the comparison.

With the above process, the backlight device 1 a can perform temperaturecorrection for the temperature drift of the red color sensor 301.

Similarly, the sensor value/BL brightness second conversion unit 502converts the detection value output from the detection unit 30 into abrightness value G of the green backlight 202. The sensor value/BLbrightness third conversion unit 503 converts the detection value outputfrom the detection unit 30 into a brightness value B of the bluebacklight 203. Next, the green color detection value temperaturecorrection unit 512 a and the blue color detection value temperaturecorrection unit 513 a performs temperature correction on the brightnessvalue of each backlight component, which has been converted in the abovemanner so that the brightness value of each backlight takes thereference value, using the information indicating the temperaturedetected by the temperature sensor 55, and the preliminarily storedcorrection equation or correction coefficient. In this manner, thebacklight device 1 uses the corrected brightness values G′ and B′ toperform temperature correction for the brightness of the green and bluebacklights as with the brightness of the red back light 201.

As described above, the backlight device 1 a of the present exemplaryembodiment compares the temperature-corrected detection values (R′, G′,and B′) of each color component of the backlight, with the target valueoutput from the backlight target value calculation unit 550, to controlthe driving signal of each backlight.

As a result, in addition to the effect of the first exemplaryembodiment, the backlight device 1 a of the present exemplary embodimentcan eliminate the BL brightness/sensor value conversion unit 520 forconverting the temperature-corrected detection value to a detectionvalue of each color sensor.

When using the backlight device 1 or backlight device 1 a of the firstor second exemplary embodiment in an image display device, it ispossible to improve color reproducibility, and therefore, there is aneffect of realizing, for example, a high-image-quality imageconfirmation display for graphic design and broadcasting purposes, and adisplay for medical purposes.

Moreover, the sensor value/BL brightness conversion unit 500 functionsas a signal filter as illustrated with Equation (1). Accordingly, thissensor value/BL brightness conversion unit 500 may be configured with ananalog circuit, a digital circuit, or a DSP (digital signal processor)or an ASIC (application specific integrated circuit).

In the present exemplary embodiments, there has been described anexample in which the light emitting unit 20 includes a red backlight201, a green backlight 202, and a blue backlight 203. However, the lightemitting unit 20 may include backlights of colors other than RGB colorssuch as CMYG (cyan, magenta, yellow, and green) colors. In this case,the detection unit 30 may include a color sensor that matches thewavelength band of the backlights provided in the light emitting unit20, and the calculation unit 50 (or 50 a) may include a sensor value/BLbrightness conversion unit 500, a temperature correction unit 510 (or510 a), a sensor target value calculation unit 530, a backlight targetvalue calculation unit 550, and a drive value calculation unit 540 (or540 a) that match the wavelength band of the backlights provided in thelight emitting unit 20.

In the present exemplary embodiments, the sensor detection value istemperature-corrected, and then it is compared with the target value.However, conversely, the target value may be temperature-corrected, andit may then be compared with the sensor detection value.

In the present exemplary embodiment, there has been described an exampleof providing a single sensor value/BL brightness conversion unit 500 anda single temperature correction unit 510. However, for example, a sensorvalue/BL brightness conversion unit 500 and a temperature correctionunit 510 may be provided for each color of color sensors.

The backlight device 1 (or 1 a) of the present exemplary embodiments maybe applied to a liquid crystal display device, a mobile informationterminal, a navigation system, an advertisement display lamp, anelectronic sign board (digital signage), or the like.

When using the backlight device 1 of the present exemplary embodiment ina liquid crystal display device, the red backlight 201, the greenbacklight 202, and the blue backlight 203 may be divided into aplurality of blocks, and lighting control may be performed individuallyfor each of the plurality of divided blocks.

A program for realizing the function of the calculation unit 50 of FIG.1 or the calculation unit 50 a of FIG. 7 of the exemplary embodimentsmay be recorded on a computer-readable recording medium, and the programrecorded on this recording medium may be read on a computer system andexecuted, to thereby perform the process of each unit. The “computersystem” includes an OS and hardware such as peripheral devices.

Moreover, the “computer system” includes a homepage provisionenvironment (or display environment) in the case of using a WWW system.

Furthermore, the “computer-readable recording medium” refers to amovable medium such as a flexible disc, magneto-optical disc, ROM(read-only memory), and CD-ROM, a USB memory connected through USB(universal serial bus) I/F (interface), and a memory device such as ahard disk drive built in a computer system. Moreover, the“computer-readable recording medium” includes one that retains a programfor a certain length of time such as volatile memory within a computersystem serving as a server or a client. The above program may realizepart of the functions described above, and further, the program mayrealize the functions described above in combination with a program thatis already recorded on the computer system.

Reference Symbols

-   1, 1 a Backlight device-   10 Backlight driving unit-   20 Light emitting unit-   30 Detection unit-   301 Red color sensor-   302 Green color sensor-   303 Blue color sensor-   40 Backlight target color setting unit-   50, 50 a Calculation unit-   55 Temperature sensor-   101 Red backlight driving circuit-   102 Green backlight driving circuit-   103 Blue backlight driving circuit-   201 Blue backlight-   202 Green backlight-   203 Red backlight-   301 Red color sensor-   302 Green color sensor-   303 Blue color sensor-   501 Sensor value/BL brightness first conversion unit-   500 Sensor value/BL brightness conversion unit-   510 Temperature correction unit-   520 BL brightness/sensor value conversion unit-   530 Sensor target value calculation unit-   540, 540 a Drive value calculation unit-   550 Backlight target value calculation unit

What is claimed is:
 1. A backlight device, comprising: a plurality oflight sources that emit light of different colors from each other; aplurality of color sensors that receive mixed-color light includinglight emitted from the light sources to detect light emission states ofthe light sources; a temperature sensor that measures a temperature in aproximity of the plurality of light sources; a brightness conversionunit that separates the mixed-color light to obtain a detection valuefor each of the light sources by converting values indicating thedetected light emission states; and a calculation unit that corrects theobtained detection value by using information indicating a relationshipbetween the measured temperature and a correction value, the calculationunit determining drive values for the light sources based on thecorrected detection value.
 2. The backlight device according to claim 1,wherein the detected light emission states include brightness values oflight according to spectral sensitivity corresponding to each color ofthe light emitted from the light sources.
 3. The backlight deviceaccording to claim 1, wherein the brightness conversion unit convertsthe values indicating the detected light emission states by using arelationship equation indicating a relationship between the detectedlight emission states and a value based on a brightness value of each ofthe light sources.
 4. The backlight device according to claim 1, whereinthe correction value comprises a value for correcting the obtaineddetection value into a detection value at a predefined temperature.
 5. Abacklight control method for a backlight device comprising a pluralityof light sources that emit light of different colors from each other,the method comprising: receiving mixed-color light including lightemitted from the light sources to detect light emission states of thelight sources; measuring a temperature in a proximity of the pluralityof light sources; separating the mixed-color light to obtain a detectionvalue for each of the light sources by converting values indicating thedetected light emission states; and correcting the obtained detectionvalue by using information indicating a relationship between themeasured temperature and a correction value, and determining drivevalues for the light sources based on the corrected detection value.